Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $55.55   6.230%   $59.0108   $59.01   $59.00   $59.00  
  Purchase #2 $184.83   8.829%   $201.1486   $201.15   $201.15   $201.10  
  Purchase #3 $203.32   10.546%   $224.7621   $224.76   $224.75   $224.80  
  Purchase #4 $165.27   10.683%   $182.9258   $182.93   $182.95   $182.90  
  Purchase #5 $132.60   5.439%   $139.8121   $139.81   $139.80   $139.80  
  Purchase #6 $135.44   6.704%   $144.5199   $144.52   $144.50   $144.50  
  Purchase #7 $156.52   5.517%   $165.1552   $165.16   $165.15   $165.20  
  7 purchase totals = $1,033.53       $1,117.3345   $1,117.34   $1,117.30   $1,117.30